s390/dasd: reshuffle struct dasd_ccw_req

Move some members of struct dasd_ccw_req to get rid of padding
bytes. This saves 16 bytes per dasd request.

Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>